Fuel filter with filter recognition

ABSTRACT

The invention relates to a fuel filter comprising a housing, an interchangeable filter cartridge that is located in the housing, a water collection chamber and a water level sensor. Said water level sensor has two electric conductors, which can be electrically interconnected by means of water if there is a correspondingly high water level. The filter is provided with a switching element that can move between a contact position and an interruption position, said switching element making contact with the two conductors in the contact position and the contact between the switching element and at least one of the two conductors is interrupted when the switching element is in the interruption position. The electric resistance that occurs between the two conductors has a first value, when the switching element is in the first contact position and a second value that differs from the first, if the switching element is in the interruption position.

The invention relates to a fuel filter according to the preamble of claim 1.

Such fuel filters are known from the prior art. They have an replaceable filter insert, as well as a cap with which the filter housing can be closed, so that when the cap is open, a so-called filter change can be performed in which the filter insert is replaced. The fuel filter has a water collection chamber in the lower area of its housing or in a suspended cap that faces downward. The specific weight of the water is greater than that of the fuel, so that the water that separates from the fuel can be collected in this water collection chamber.

The increasing precision with which fuel injection systems are manufactured makes components that are used and the cross-sections for fuel lines increasingly sensitive to contaminants in the fuel. It is particularly dangerous, for example, when the filter insert having the filter surface is removed from the fuel filter during a so-called filter change and subsequently, for example, following a pause in operation, the filter housing is reclosed without installing an unused filter insert, or after inserting a non-approved filter insert, whose measurements, for example, are too small, or which has a filter surface that is unsuitable for the type of fuel that is used.

In such cases, insufficiently filtered or completely unfiltered fuel, together with dirt particles and other contaminants, can get into the highly sensitive fuel-injection system.

The undesirable fuel contaminants also include water, which, for example, as a consequence of the temperature change between daytime and nighttime temperatures, forms as condensation from the atmospheric humidity from the volume of air that is in a fuel tank. The operator of an internal combustion engine using the fuel or maintenance personnel can hardly influence or avoid this formation of condensation. For this reason, a water level sensor is provided as a safety measure in a conventional fuel filter. The sensor is formed by two electrical contacts that are spaced apart from one another and arranged high up in the water collection chamber. The electrical conductivity of water differs from that of fuel and, when the water level in the water collection chamber rises above a specified value, the water short-circuits the two contacts, thereby significantly altering the electrical resistance between the two contacts.

The value of the electrical resistance can thus be described as the “short-circuit value” when the two conductors are electrically connected to one another by means of the water found in the fuel filter, and the value of the electrical resistance described as the so-called “insulation value” when the two conductors are separated from one another or are connected to one another only by the fuel or by insulating materials.

The change from the “insulation value”, which corresponds to the normal operation of the fuel filter, to the “short-circuit value”, when the water content in the fuel filter is too high, is measured and evaluated by an electronic switch, whereby the switch, for example, can be part of an electronic motor control unit. In the field of automobile construction, it is well-known to trigger an optical and/or acoustical signal within the driver's perceptual range when water in the fuel filter reaches a defined level.

A more far-reaching measure can also be provided, however, which, in order to protect the internal combustion engine, automatically prevents the motor from being started, for example, when an unacceptably high amount of water in the fuel filter is ascertained, in order to protect, in this way, the fuel injection system of the motor and to prevent water from reaching the clean side of the fuel filter and getting into the fuel injection system. After the water has been drained, when the “short circuit” caused by the water between the two contacts of the water level sensor no longer exists, the electronic control evaluates the higher electrical resistance that now prevails, so that, for example, it now is possible to restart the motor.

It is well-known in the field that, irrespective of the aforementioned water level sensors, temperature sensors or pressure sensors can be provided in the fuel filter. Depending upon the construction of the filter, one, two, or all three of the aforementioned sensor types may be provided in one fuel filter.

The task of the invention is to improve a generic fuel filter and specify a process in a way that enables the fuel filter to provide better protection for the engine associated with the fuel filter, with the least possible technical complexity and expense.

This task is solved by a fuel filter with the features of claim 1 or by a switch element according to claim 11 or by a filter insert according to claim 12 or by a procedure for changing a filter insert according to claim 13 or by a diagnostic procedure according to claim 17.

In other words, the invention proposes using an electrical switch, such as the motor control unit that is customarily provided anyway, to detect the presence or absence of the filter insert in the fuel filter. For this purpose, an electrical conductor is provided the electrical properties of which change as a function of the presence or absence of the filter insert. For example, the electrical resistance values can change when the electrical conductors are interrupted or closed, as a function of the assembly status of the filter insert, or the electrical capacitance values can change, as a function of the assembly status of the filter insert.

Because the electrical conductor is connected to the electrical switch, it can evaluate the electrical resistance or capacitance values and properly assume an “operative” switch state or an “inoperative” switch state. The “inoperative” switch state can, as previously mentioned, result in a signal displayed to the personnel or in an automatic shutdown of the internal combustion engine.

For example, a switch contact can be provided in the fuel filter that is similar to a pushbutton or a door contact switch, whereby the switch contact is depressed when the filter insert is present and two contacts of the electrical conductor open or close, depending upon the construction of the switch contact, and whereas, when the filter insert is missing, the switch contact assumes its other switch position accordingly.

Advantageously, a separate electrical conductor does not have to be provided, but rather, an electrical conductor that is already provided anyway may be used. This can be advantageously a conductor that is continuously connected to a sensor that is provided in the fuel filter or at least is then connected when the filter insert is present in the fuel filter.

In a fuel filter that is known from the prior art and is equipped with a water level sensor, the two electrical conductors that belong to the water level sensor anyway can also be used advantageously to indicate the presence of a fuel filter insert. In this way, the water level sensor can be used to indicate an actual presence in the fuel filter of the replaceable filter insert, which is provided for this fuel filter, completely independently of the monitoring of the water level in the fuel filter. This monitoring is also done by evaluating the electrical resistance between the two electrical conductors of the water level sensor.

According to the proposal, a switch element is provided for this purpose. The switch element is moveable and, on the one hand, can assume a contact position in which it makes contact with the two electrical conductors. On the other hand, the switch element can assume an interrupt position, in which this connection between the two electrical conductors of the water level sensor is interrupted when the switch element is not in contact with at least one of the two conductors.

The switch element provided according to the proposal can be constructed as a component that is separate from the rest of the filter, for example, in the form of a disk, a pin, or something similar. This separate component can, for example, be handled by an assembly worker in the factory during the manufacture of the fuel filter. After the filter has been properly assembled, the assembly worker inserts this separate switch element into the fuel filter, for example, before he closes the filter housing with a cap. By inserting this separate switch element, more or less a type of quality control, the assembly worker confirms that the filter is properly assembled and, if applicable, is properly connected to adjacent components.

If, for example, the two electrical conductors of the water level sensor make contact with each other in the factory, that is, they would create a “short-circuit value”, then the insertion of the switch element into the fuel filter creates a separation of these two conductors. Within the framework of the existing proposal, an electrical resistance that can be measured between the two conductors and that is higher than the “short-circuit value” is referred to as a “separation”. If the switch element is not inserted, then the two conductors are short-circuited, comparable to an unacceptably high water level in the water collection chamber. As a result, regardless of whether or not water is actually in the fuel filter, the electronic control evaluates the electrical resistance of the water level sensor as it would if there were an unacceptably high water level and, in this way, for example, prevents a motor connected to the fuel filter from starting or triggers a warning signal.

If, however, the two electrical conductors of the water level sensor were separated from one another in the factory, for example, that is, would present an “insulation value”, provision can be made for the switch element to represent an electrical bridge that connects the two electrical conductors of the water level sensor.

The construction of the switch element as an electrical bridge can, for example, be provided when the switch element is moveably mounted within the fuel filter and automatically attempts to assume a contact position, for example, is pushed into its contact position by force of gravity or a spring force. The switch element would assume this position, when there is no filter insert in the fuel filter. When the switch element is constructed as an electrical conductor with good conductivity and negligibly low electrical resistance, this position corresponds to the short-circuit situation when the water level in the fuel filter is unacceptably high. Such a switch element is moved against the gravitational force or spring force from its contact position into its interrupt position only when the filter insert is assembled, so that now a short circuit between the two electrical conductors of the water level sensor is avoided and signals are present in the electronic control unit, which signal the proper operation of the fuel filter.

In an embodiment in which the switch element is constructed as an electrical bridge, the switch element may advantageously be intentionally constructed not as an electrical conductor with good conductivity and negligibly low electrical resistance, but rather, as an element with a defined electrical resistance that is different from that of the short-circuit value and also from that of the insulation value. Such a third value, which can take on the electrical resistance between the two conductors, is called the “filter insert value”. Compared to the usual evaluation of the sensor signals of the water level sensor, this provides additional information which can be automatically evaluated, for example, by means of the electronic switch, for example, a motor control unit.

This defined resistance enables automatic recognition of three different states of the fuel filter, assuming that the electronic control is constructed accordingly.

a) First, the occurrence of an unacceptably high water level within the water collection chamber of the filter is recognizable.

In this case, namely, a short circuit exists.

b) Secondly, the presence of a specified filter insert in the fuel filter is recognizable.

In this case, namely, whereby the embodiment of the fuel filter is according to a first alternative, after a filter change, the defined resistance value exists as the “filter insert value”, when the switch element is constructed such, that it is moved into its contact position when the filter insert is inserted, which creates a bridge between the two conductors of the water level sensor with its defined electrical resistance.

Or, in this case, with an embodiment of the fuel filter according to a second alternative, the insulation value exists after a filter change when, namely, the switch element is constructed such that when the filter insert is inserted, the switch element is moved from its contact position into its interrupt position, thereby no longer providing a bridge between the two conductors of the water level sensor.

c) Thirdly, the absence of the filter insert in the fuel filter is recognizable.

In this case, namely, according to the aforementioned first alternative, the insulation value is present, because the switch element is constructed such that it should have been moved into its contact position when the filter insert was inserted. If this does not occur, because no filter insert was inserted into the fuel filter, there is no bridge between the two conductors of the water level sensor.

Or, in this case, according to the aforementioned second alternative, the “filter insert value” is present after a filter change, because the switch element with its defined resistance continues to be in its contact position and has not been moved into its interrupt position by the insertion of the filter insert.

According to the aforementioned first alternative, the fuel filter and the switch element can hereby advantageously be constructed such that the switch element provides a defined electrical resistance between the two conductors of the water level sensor when the filter insert is properly fitted in the fuel filter. If the two conductors had previously been either separated from each other or connected to one another, that is, the electrical resistance between them indicated the insulation value or the short-circuit value, they will be electrically connected to one another by the switch element, and, indeed, with a resistance value that corresponds neither to the insulation value nor to the short-circuit value, but rather is referred to as the filter insert value.

Particularly when the switch element is handled together with the filter insert, for example, is constructed as a part of the filter insert, different filter inserts may automatically be distinguished from one another in this way by using correspondingly different electrical resistances in their switch elements. Thus, for example, it can be advantageous to use basically an identical construction of the fuel filter in a most cost-effect manner for use with several different types of vehicles or motors or fuels.

For example, the construction can be such that basically the same fuel filter is used for either gasoline or diesel engines. Or the fuel filter can be used with either mineral fuel or biodiesel fuel made of vegetable raw materials. Or the fuel filter can be installed in vehicles targeted for delivery to different geographical regions with differing fuel qualities.

With basically an identically constructed fuel filter, it may be intended to use other filter inserts, for example, filter inserts in which the filter surface is made of different materials having different filter meshes or different degrees of durability to certain substances. Depending upon the planned area of application or the planned construction of the motor, the electronic control of the respective motor is adjusted in the factory to a certain filter type, that is, to a certain one of several different filter inserts, so that the switch element must have a predetermined electrical resistance in the fuel filter, in order to enable a proper operation of the motor.

If a non-specified electrical resistance is determined, provision can be made such that either the motor control unit prevents the motor from being started, or that shorter maintenance intervals are specified, so that corresponding warnings that are displayed to the operator of the motor are displayed after a correspondingly shorter period of operation than is normally the case, or an indication may be provided to the operator of the motor that the filter insert is missing or that an incorrect, non-specified filter insert is installed.

For this reason, a procedure according to the proposal for changing the filter insert of a fuel filter is characterized in that the electrical resistance between the two electrical conductors of the water level sensor is altered simultaneously with the assembly or removal of the filter insert.

For a water level sensor with two conductors touching each other, this means that, when a filter insert is removed, a switch element, which had thus far separated the two conductors from one another, is also removed from the fuel filter, so that now the two electrical conductors come into contact with each other and result in the same electrical short-circuit value of the sensor that would result, when the two electrodes of the water level sensor are bridged by water.

For the conventional construction of a water level sensor, in which two electrical conductors are separated from one another, during the process of changing a filter insert according to the proposal, provision may be made for the switch element to be moved into its contact position when the filter insert is removed from the fuel filter, so that now the two electrical conductors of the water level sensor are bridged.

If no new filter insert is inserted into the fuel filter, then in both aforementioned cases, following maintenance work, the same electrical resistance between the two conductors of the water level sensor will prevail, as if the two electrodes of the water level sensor were short-circuited by water standing in the fuel filter, namely, the short-circuit value. The corresponding electronic control, for example, a motor control unit, thus automatically reacts the same as it does to an excessive amount of water in the fuel filter. Therefore, according to the proposal, a procedure is specified for changing a filter insert, which, with the same handling of the filter insert, i.e., without more work required during maintenance, improves the safety for the operation of the filter and the safety for the technical device to be protected by the filter, for example, an internal combustion engine.

Also a diagnostic procedure for checking a fuel filter is characterized according to the proposal, in that the electrical resistance between the two electrical conductors of the water level sensor is altered, depending upon whether or not a filter insert is installed in the fuel filter. In this way, additional information can be gained and the operational safety of the fuel filter, as well as its associated aggregate using the fuel, can be improved with very small changes to existing systems, both with respect to the fuel filter and to the electronic switches that evaluate the signals of the water level sensor.

In a particularly advantageous embodiment, provision can be made during the diagnostic procedure for, as mentioned above, not only two switching states to be considered, but rather three, for example:

-   -   first, “short circuit” with very low or no electrical resistance         between the two electrical conductors of the water level sensor.         Depending upon the structural design of the fuel filter, this         resistance value can, for example, be caused by an excessively         high water level in the fuel filter or by the absence of a         filter insert;     -   second, a “correct resistance”, depending upon the predetermined         electrical resistance. Depending upon the structural design of         the fuel filter, this “correct resistance” can be the resistance         value that the switch element has, for example, in the form of         the “filter insert value” when an approved filter insert is         present in the fuel filter, wherein this “correct resistance”         can, however, alternatively also be the “insulation value” when,         for example, the filter insert mounted in the fuel filter merely         separates the two conductors, but does not itself create an         electrical connection between them;     -   and, third, a switching state of “incorrect filter insert”,         when, namely, an electrical resistance of the switch element is         determined that does not correspond to the short-circuit value,         but also not to a specified electrical resistance of the switch         element, so that this “incorrect” resistance value signals that         a filter insert is installed that is improper and not intended         for this motor.

The aforementioned switch element can be constructed on the filter insert itself. The filter insert can be conventionally constructed, that is, in the known manner, it can have a filter medium, such as a folded paper filter insert, and mechanically more stable components, made of plastic, such as, for example, a frame, or an upper and a lower end plate, or a so-called interior dome in the form of a tube-like component, which supports the filter medium that is arranged circumferentially around it against the forces exerted on it during the filter operation. In such cases, the switch element can advantageously be provided on the mechanically more stable components of the filter insert, for example, on an end plate or on the interior dome.

The switch element can, however, also be constructed as a separate component. This can, for example, be installed by an assembly worker or a mechanic as a separate component in the fuel filter, as described using the aforementioned disk or pin. Alternatively, provision can be made for such a separate component, also designated “adapter”, to be attached to a filter insert, so that afterwards, when the filter insert is installed, the adapter, which carries the switch element, is also automatically installed into the fuel filter. In this way, the mechanic can easily connect the switch element to the filter insert outside of the fuel filter, for example, outside the confined space of a vehicular engine compartment, and the filter insert can subsequently be installed into the fuel filter in the known manner, so that the handling of the switch element does not unnecessarily complicate the filter change for the mechanic.

Embodiments of the invention are explained in more detail below, based on the purely schematic drawings. Accordingly,

FIG. 1 shows a cross-section through a filter insert including, the water level sensor of a first embodiment, whereby other components of the fuel filter having the filter insert are not shown for purposes of clarity;

FIG. 2 shows the water level sensor in an enlarged version compared to FIG. 1;

FIGS. 3 to 5 show a switch element of the FIG. 1 arrangement on an enlarged scale compared to FIG. 1 and from three different views;

FIGS. 6 and 7 show a partially broken-out cross-section similar to FIG. 1, but with a second embodiment;

FIGS. 8 and 9 show views similar to FIGS. 6 and 7, but with a third embodiment;

FIG. 10 shows a view similar to FIG. 1, but with a fourth embodiment; and

FIGS. 11 to 20 show longitudinal cross-sections through four other embodiments of filters, each in a view with and without a filter insert being present in the filter.

FIG. 1 shows a filter insert 1, which is essentially constructed in a known manner as a cylinder and has an upper end plate 2 and a lower end plate 3, wherein these two end plates 2 and 3 are made of plastic. Between the end plates, the filter insert 1 has a filter surface, which is referred to as a filter medium 4. The filter surface can be constructed in conventional manner, for example, as a pleated filter made of a paper or synthetic material.

In the embodiment shown, the filter insert is used in a suspended fuel filter, i.e., in a fuel filter whose cap is not arranged on the upper end of the filter housing, but rather on the lower end. The filter insert 1 is accordingly inserted into the filter housing from the bottom up and slid thereby onto a connection piece 5 that has two electrodes 6 on its lower end, which are part of a water level sensor that is indicated as a whole with 7.

Radially inside the lower end plate 3, the filter insert 1 has a rotating, upward-extending collar 8 that is sealed against the connection piece 5 with a gasket 9. The collar 8 is constructed such that, when inserting the filter insert 1 into the fuel filter, it makes contact from below with a sliding sleeve 10. The sliding sleeve 10 surrounds the connection piece 5 and is mounted on the piece so as to slide longitudinally along it. Inserting the filter insert 1 into the fuel filter pushes the sliding sleeve 10 farther upward on the connection piece 5.

The sliding sleeve 10 is pressed downward by a helical spring 11, thereby automatically forcing the sleeve 10 to assume a position that is lower than the one shown in FIG. 1, when there is no filter insert 1 in the fuel filter. When the filter insert 1 is inserted, the sliding sleeve 10 is pushed upward on the connection piece 5, against the force of the helical spring 11, into the position shown in FIG. 1, as previously described.

Gravity also urges the sliding sleeve 10 to automatically take the aforementioned lower position, when there is no filter insert 1 in the fuel filter. Deviating from the embodiment shown, it is also possible that only this gravitational force be used. Advantageously, in the embodiment shown, the force effect of the helical spring 11 is particularly reliable in ensuring the desired movement of the sliding sleeve 10. Furthermore, this arrangement, that is, with the helical spring 11, can also be used for an arrangement of the filter insert 1 in which the filter insert 1 is inserted into the fuel filter from above, and the sliding sleeve 10 should therefore be raised when there is no filter insert 1 in the fuel filter.

The sliding sleeve 10 has a U-shaped flexible tongue 12 inside, which makes contact with the connection piece 5 and will be discussed in more detail below. The flexible tongue 12, or the flexible tongue 12 in conjunction with the sliding sleeve 10, represents the switch element. This switch element uses two electrical conductors 14 of the already provided water level sensor 7, in order to be able to detect the presence of the filter insert 1 in the liquid filter, as will be explained below in more detail.

FIG. 2 shows the connection piece 5 without the filter insert 1 surrounding it and in the same proportions as shown in FIG. 1, which are not true to scale. The connection piece 5 is made of an electrically insulating material, such as a suitable fuel-resistant plastic. Two electrical conductors are molded into the connection piece 5. A dotted line shows where the conductors 14 are each circumferentially surrounded by the material of the connection piece 5, that is, are insulated all around. On the other hand, on a certain section of the connection piece 5, the conductors reach the surface of the connection piece 5, wherein they are spaced apart from one another and thus separated electrically. In FIG. 2 these two sections of the conductors 14 are indicated by continuous lines. With their two lower ends, the conductors 14 form the two electrodes 6 of the water level sensor 7 at that point where they protrude from the lower end of the connection piece 5. Deviating from this embodiment, the electrodes 6 can be made of another material than the conductors 14, for example, of an especially oxidation-resistant material.

On its lower end, the connection piece 5 has a stop 15. This can take the form of several projections spaced radially about the connection piece or of a continuous, circular flange. The stop 15 cooperates with the sliding sleeve 10 such that it restricts the downward movement of the sleeve. Under the force effect of the helical spring 11 and gravity, the sliding sleeve therefore moves only so far downward until it makes contact with the stop 15.

FIGS. 3 to 5 illustrate the sliding sleeve 10 and the flexible tongue 12 arranged therewithin. The sliding sleeve 10 is dimensioned so that it can be pushed onto the connection piece 5, for example, from above, before the connection piece 5 itself is assembled in the housing of the fuel filter. The selected geometry of the connection piece 5 and the sliding sleeve 10 structurally ensure that the sliding sleeve 10 can be placed on the connection piece 5 in only one specific angular position, for example, by means of a protrusion on one component and a groove on another component or by means of a basically unround contour of the connection piece 5 and sliding sleeve 10, so that the sliding sleeve 10 can be assembled on the connection piece 5 in only one angular position.

The inside of the sliding sleeve 10 receives the flexible tongue 12. FIG. 5 shows that the flexible tongue 12 has a U-shaped construction and two longer, parallel arms, as well as a shorter cross-bar that connects the two arms. As illustrated in FIG. 3, the flexible tongue 12 is attached to the wall of the sliding sleeve 10 by its cross-bar, whereas the two arms of the flexible tongue 12 extend into the inside of the sliding sleeve 10 and away from its wall. The sliding sleeve 10 can, for example, be made of plastic and constructed as an injection molded component, while the flexible tongue 12 is constructed to conduct electricity, for example, is made of metal.

A pin that projects inward on the wall of the sliding sleeve 10, when used in conjunction with a bore in the cross-bar of the flexible tongue 12, can serve to affix the flexible tongue 12 to the sliding sleeve 10. The pin is thus welded onto the sliding sleeve.

An alternative fastening by means of screwing, riveting, and the like is, however, also possible, in order to affix the flexible tongue 12 in the sliding sleeve 10, as illustrated in FIGS. 3 to 5. Deviating from the embodiment shown, the flexible tongue 12 may also be placed into the casting mold of the sliding sleeve 10 and, during the manufacture of the sliding sleeve 10, to injection-mold around the tongue with the basic material of the sleeve, so that no additional fastening means is required.

With respect to its angular position, the sliding sleeve 10 is arranged on the connection piece 5 such that the two arms of the flexible tongue 12 make contact with the two electrical conductors 14 when the sliding sleeve 10 is placed at the corresponding section of the connection piece 5.

In the case of the embodiment shown, the sliding sleeve 10 is pressed downward and against the stop 15 by the helical spring 11. Because the conductors 14 run along the inside of the connection piece 5 in its lower area, the arms of the flexible tongue 12 do not make contact with the conductors 14, so that the conductors 14 are not bridged by the flexible tongue 12. The switch element that is formed by the flexible tongue 12, or by the sliding sleeve 10 together with the flexible tongue 12, thus assumes its interrupt position when there is no filter insert 1 located in the fuel filter.

By contrast, the switch element assumes its contact position when the filter insert 1, according to FIG. 1, is assembled in the fuel filter. When the filter insert 1 is assembled, the sliding sleeve 10 is raised, and the two arms of the flexible tongue 12 move into the area of the connection piece 5 in which the two electrical conductors 14 extend along the surface of the connection piece 5, so that the flexible tongue 12 provides an electrically conducting bridge between the electrical conductors 14.

The flexible tongue 12 is made of an electrically conducting substance, for example, a metallic material, but it has a defined electrical resistance. In its contact position, it therefore connects the two electrical conductors 14 with a resistance that can be evaluated by the electronic switch, which also evaluates the signals of the water level sensor 7. By means of the measured electrical resistance, a diagnosis can be made regarding

-   -   whether the fuel filter is in an operational state that can be         designated as “OK” when, namely, a filter insert 1 is present in         the fuel filter and there is no, or only a little, water in the         fuel filter, because then the defined electrical resistance of         the switch element can be measured between the two electrical         conductors 14,     -   or whether the fuel filter is in an operational state that can         be designated as “not OK” because, namely, there is too much         water in the fuel filter, because then the “short-circuit value”         of the electrical resistance can be measured between the two         electrical conductors 14, because the electrical current will         not flow through the comparatively higher electrical resistance         of the switch element,     -   or whether the fuel filter is in an operational state that can         likewise be designated as “not OK” because, namely, there is no         filter insert 1 in the fuel filter, because then the “insulation         value” of the electrical resistance can be measured between the         two electrical conductors 14, because the switch element nor the         water create a bridge between the two electrical conductors 14.

In one of the embodiments that differs from the embodiment of FIG. 1, provision can be made according to the embodiment of FIG. 10 so that, in'the lower region of the connection piece 5, the conductors 14 extend along the surface of the connection piece 5. In this case, the arms of the flexible tongue 12 make contact with the conductors 14 when the filter insert 1 has been removed from the fuel filter and the sliding sleeve pressed by the helical spring 11 onto the lower end of the connection piece 5 and against the stop 15.

The flexible tongue 12 is also constructed differently from the embodiment of FIG. 1 and does not have a defined resistance of a specific, average magnitude, but in the embodiment of FIG. 10, it instead has an optimum electrical conductivity with a very low resistance. When the flexible tongue 12 is in the aforementioned contact position, the switch element thus causes a short circuit between the two electrical conductors 14 that is comparable to a water level inside the fuel filter that would connect the two electrodes 6 of the water level sensor 7 with one another.

When the filter insert 1 is removed from the fuel filter, the electrical switch assumes the same switching state as it would for an unacceptably high water level in the fuel filter, so that, for example, a warning signal would be triggered or the start of the engine would be prevented. On the other hand, in the embodiment of FIG. 10, when the filter insert 1 is inserted, the sliding sleeve 10 is raised and shifted into the interrupt position of the switch element, in which, namely, the two electrical conductors 14 are not connected to each other by the flexible tongue 12, because the arms of the flexible tongue 12 make contact externally with the non-conductive material of the connection piece 5.

Within the framework of another not shown modification of this basic embodiment of FIGS. 1 and 10, provision can be made in an embodiment that otherwise corresponds to the one in FIG. 10 for the flexible tongue 12 not to have optimum electrical conductivity with very low electrical resistance, but instead to have a defined resistance of average magnitude. Thus, an electrical connection is in fact created, but there is no short circuit between the two electrical conductors 14 when the filter insert 1 has been removed from the fuel filter and the sliding sleeve 10 has been pressed by the helical spring 11 onto the lower end of the connection piece 5 and against the stop 15, and connects the two electrical conductors 14 to one another. By means of a corresponding switch, for example, the motor control unit, different operating states of the fuel filter can therefore be detected by means of the different electrical resistances:

-   -   For example, “Filter insert improperly installed”—in the case of         a high electrical resistance, when the flexible tongue 12 is         separated from the two electrical conductors 14 and makes         contact with the electrically insulating material of the         connection piece 5; or     -   “Water level unacceptably high”—in the case of a very low         electrical resistance or a short circuit, when the electrodes 6         of the water level sensor 7 are short-circuited by water when         the water level is unacceptably high; or     -   “Filter insert missing”—in the case of an average electrical         resistance, when the flexible tongue 12 makes contact with the         two electrical conductors 14 and connects them with the defined         resistance of the flexible tongue 12.

Basically, the sliding sleeve 10 and the helical spring 11, as shown in FIGS. 1 to 5, can be provided with a fixed filter. For example, according to the embodiment shown, these components can be affixed to the connection piece 5, or they can be affixed to a protective dome that is provided in the inside of the fuel filter and that prevents the filter medium 4 from collapsing under the temperatures and pressures that prevail during operation of the fuel filter.

As an alternative to this, the switch element can be provided on the replaceable filter insert. In this way, a designation that is typical for different filter inserts can be made possible by means of correspondingly different electrical resistances, which the respective switch elements have. FIGS. 6 to 9 show extremely simplified embodiments of this type.

FIG. 6 illustrates a filter insert 1 that holds a fin 16, which is oriented upward, on an upper end plate 2. The two electrical conductors 14 that extend from the lower electrodes 6 through the connection piece 5 are constructed in the form of a pair of spring clips, which, when the filter insert 1 is not assembled in the fuel filter, lie against each other due to their form and their spring-elasticity. As a purely schematic drawing, FIG. 6 does not illustrate how the upper end of the connection piece 5 is affixed in the housing of the fuel filter, and FIG. 6 also does not illustrate in detail how the course of the two electrical conductors 14 actually extends in the transition section from the connection piece 5 to the housing of the fuel filter. These figures should merely schematically illustrate that, by inserting the filter insert 1 into the fuel filter, the fin 16 is guided as a separator between the two electrical conductors 14. Without the filter insert 1, the short-circuit value of the electrical resistance between the two conductors 14 is achieved, so that the electronic switch assumes the same switch state as it does for an unacceptably high water level in the fuel filter.

The embodiment of FIG. 6 is shown in a top view in FIG. 7. The view onto the upper end plate 2 of the filter insert 1 shows the fin 16 that is situated between the two spring-clip-like electrical conductors 14 and that separates them from one another.

The fin 16 can be made of plastic and, for example, be manufactured as a single piece with upper end plate 2 using the injection molding process. Selecting a suitable plastic material allows the fin 16 to insulate the two electrical conductors 14 from each other.

The fin 16 can, however, also be manufactured using another material that has no insulating properties, but has a significantly higher electrical resistance relative to the short-circuit value, so that the electrical resistance between the two conductors 14 assumes a “filter insert value” when the filter insert 1 is inserted in the fuel filter.

Instead of a special material for the fin 16, the fin 16 can also be manufactured from insulating material, that is, electrically conductive surfaces in the form of electrical contacts can be provided on both sides of the fin 16, and these contacts can be connected with a defined electrical resistance, so that, in this case, too, the fin 16 does indeed act as a separator, but does not insulate the two electrical conductors 14 from each other, but instead, separates them by means of a defined electrical resistance, so that, in this case, too, the electrical resistance assumes a “filter insert value” when the filter insert 1 is in the fuel filter.

The embodiment in FIGS. 8 and 9 shows an alternative mounting possibility for a fin 16. Here, a groove 17 that opens at the lower end of the connection piece 5 is provided in the connection piece 5. The fin 16 is provided inside the filter insert 1, whereby, in this embodiment, the filter insert 1 has an interior dome 18, that is, a tube-shaped, fluid-permeable protective body for the filter medium 4, which, unlike a protective dome with a fixed filter, is part of the filter insert 1 and is replaced together with the filter insert 1. The two electrical conductors 14 enter into the inside of the groove 17 at a predetermined height of the connection piece 5, that is, they lie there exposed. In the embodiment in FIGS. 8 and 9, they are constructed as spring clips that make contact with each other and are separated from each other by the fin 16 when the filter insert 1 is inserted, similar to how this is described using the embodiment of FIGS. 6 and 7.

In the embodiments in FIGS. 6-9, a differential diagnosis of the fuel filter states is possible when the two electrical conductors 14 are not in contact with each other, but are instead spaced apart as long as the filter insert 1 is not inserted into the fuel filter. When the filter insert is not inserted, the two electrical conductors 14 are insulated from each other because they do not touch, and, based on the insulation value of the electrical resistance, it can be measured and diagnosed that no filter insert is in the fuel filter. When the filter insert is inserted into the fuel filter, however, the defined electrical resistance in the area of the fin 16 causes the two electrical conductors that are connected to each other by the fin 16 to indicate this “filter insert value” of the electrical resistance, so that, accordingly, the presence of the filter insert can be automatically determined. When, by contrast, a measurable short circuit exists between the two electrical conductors 14, then too much water is in the fuel filter and the two electrodes 6 are short-circuited with each other by this excessively high water level.

FIG. 11 illustrates a section of a filter with a filter housing 19, which is suspendingly mounted and has a screw cap 20 arranged on the bottom that closes the filter housing 19. The screw cap 20, with its threaded circular wall, pushes against the lower end plate 3 of the filter insert 1 and holds this plate in its predetermined position.

Two electrodes 6 extend downward on the connection piece 5, the lower ends of which form the water level sensor 7. When, in the embodiment shown, water collects in the lower area of the filter housing 19, particularly in the area of the screw cap 20, due to its higher, specific weight, and the level of this water reaches a corresponding level, then the water can pass through openings that are provided in a downward-projecting cup 22, wherein this cup 22 is formed by the lower end plate 3. The cup 22 has a central pin 23 that extends between the two electrodes 6 of the water level sensor 7 and thereby prevents a short-circuiting of these two electrodes 6. The short circuit is much more frequently caused by the water found in the filter housing 19 when the water level is correspondingly high, so that, in such a case, the water level sensor 7 emits the alarm.

FIG. 12 illustrates the same embodiment as FIG. 11, although in a state in which the filter housing 19 is closed with the screw cap 20, without the filter insert having been inserted into the filter housing 19. The two electrodes 6 are made of spring-elastic wires or spring-elastic metal strips, each of which is bent into an approximate J-shape on its free end. If these free ends of the electrodes 6 are not pressed apart by the pin 23 of the filter insert 1, they make contact with each other and cause the water level sensor 7 to short-circuit, so that the same alarm signal is generated as would be when an unacceptably high water level is present in the filter.

FIG. 13 illustrates an embodiment in which the lower area of the filter housing 19 is again shown in a longitudinal cross-section. This particular filter, however, is assembled upright, and thus has a screw cap on the upper area of the filter 19, so that this screw cap is not visible in the selected drawing.

The water level sensor 7 is formed by two electrodes 6, which, similar to the embodiment in FIGS. 11 and 12, are constructed as wire clips bent into J-shapes. In the drawing according to FIG. 13, the filter housing 19 is shown without an inserted filter insert.

FIG. 14, by contrast, illustrates the same embodiment with an inserted filter insert 1. The lower end plate 3 of the filter insert 1 forms a circumferential collar 24, which supports an external actuation ring 26 by means of a snap contour 25. When the filter insert 1 is inserted a sufficient distance into the filter housing 19, this actuation ring 26 extends between the two electrodes 6 of the water level sensor 7 and prevents them from short-circuiting, as long as the water level in the filter housing is not correspondingly high.

FIG. 15 illustrates another embodiment of a suspended filter arrangement. As in FIGS. 11 and 12, the screw cap 20 is provided here on the downward-opening filter housing 1. The electrodes 6 of the water level sensor 7 are constructed as pins. In the screw cap 20, there is a cap spring 27 that is constructed as a helical spring and supports a contact body 28. When, as shown in FIG. 15, no filter insert is arranged in the filter housing 19, the contact body 28 is pressed against the two ends of the electrodes 6 by the cap spring 27. At least in the area of this contact surface, in which the contact body 28 makes contact with the two electrodes 6, the contact body 28 is conductive, so that it short-circuits the two electrodes 6 and causes a signaling of the water level sensor 7.

FIG. 16 illustrates the embodiment of FIG. 15 with an inserted filter insert 1. Also in this embodiment, the lower end plate 3 of the filter insert 4 forms a cup 22 with openings 21. The cup 22 pushes the contact body 28 downward against the force of the cap spring 27 and holds the contact body 28 a distance away from the water level sensor 7.

Deviating from the embodiment illustrated in FIGS. 15 and 16, the contact body 28 can be eliminated and, in its place, the cap spring 27 can be constructed such that the cap spring itself makes contact with the electrodes 6 and short-circuits these two electrodes 6 when no filter insert 1 is inserted. For this purpose, on its end where it makes contact with the cup 22 or the electrodes 6, the cap spring 27 can have spring windings that, when compared to the always identical diameter as illustrated, have a decreasing diameter.

In the embodiment of FIGS. 17 to 20, a suspended filter is again illustrated, with a lower screw cap 20. The connection piece 5 has a pin-like water level sensor 7 on its lower end, as well as a spring-elastic contact wire 29 that is affixed on one end in the connecting piece 25 and has a second end that is freely moveable. The contact wire 29 is hereby bent as shown in FIG. 17 such that, it makes contact with the water level sensor 7 and causes a short circuit of its electrodes, and thus, effects an alarm of the water level sensor 7, when no filter insert is in the filter housing 19.

In comparison, FIG. 18 illustrates the situation when a filter insert 1 is in the filter housing 19. In this embodiment, too, the lower end plate of the filter insert 1 forms a cup 22 that has openings 21. The cup 22 also forms a circumferential, inward-protruding projection 30, which makes contact with the freely movable end of the contact wire 29. The contact wire 29 is hereby bent such is now spaced a distance apart from the water level sensor 7.

FIG. 19 illustrates the configuration of FIG. 17 in the area of the water level sensor 7 on an enlarged scale. One of the ends of the contact wire 29 is affixed in the connection piece 5, whereas its other, angled end is freely movable. In its mid-section, the contact wire 29 forms a 180° hairpin-shaped curve and makes contact with the water level sensor 7 in this area.

FIG. 20 illustrates the situation similar to FIG. 18, however, also on an enlarged scale. The circumferential shoulder 30 of the cup 22 of the lower end plate 3 touches the free, curved end of the contact wire 29. When the filter insert 1 is inserted far enough into the filter housing 19, the contact of the projection 30 with the contact wire 29 causes the contact wire to bend such that it is bent away from the water level sensor 7 into its position away from the water level sensor 7, that is shown in FIGS. 18 and 20. 

1. Fuel filter of an internal combustion engine, with a housing, a filter insert replaceably arranged in the housing, and at least one electrical conductor that is connected to a switch, wherein, depending upon the respective electrical value, the switch assumes an “OK” switch state or a “not OK” switch state, characterized in that the electrical conductor (14), depending upon whether the filter insert (1) is inside or outside of the filter, has different electrical resistance and/or capacitance values, and the switch assumes a “not OK” switch state when the filter insert (1) is outside of the fuel filter.
 2. Fuel filter according to claim 1, characterized in that when the filter insert (1) is inside the fuel filter, the electrical conductor (14) is connected to a sensor that is provided in the fuel filter.
 3. Fuel filter according to claim 2, characterized by a water collection chamber and a water level sensor (7), wherein the water level sensor (7) has two electrical conductors (14) that are electrically connectible to one another by the water when the water level is correspondingly high, and by a switch element that is moveable between a contact position and an interrupt position, wherein the switch element in its contact position makes contact with the two conductors (14), the contact of the switch element with at least one of the two conductors (14) is interrupted when the switch element is in its interrupt position, and the electrical resistance between the two conductors (14) has a first value when the switch element is in its contact position and a second value that differs from the first when the switch element is in its interrupt position.
 4. Fuel filter according to claim 3, characterized in that the two conductors (14) of the water level sensor (7) contact each other when the filter insert (1) is outside of the fuel filter, and the switch element is constructed as an electrical separator, which is insertable into the fuel filter and between the two conductors (14), the switch element in its contact position separating the conductors (14) from each other.
 5. Fuel filter according to claim 3, characterized in that the two conductors (14) of the water level sensor (7) are separated from one another when the filter insert (1) is outside of the fuel filter, and the switch element is constructed as the electrical connector, which is insertable into the fuel filter and, in its contact position, electrically connects the two conductors (14) to one another.
 6. Fuel filter according to one of the preceding claims, characterized in that the switch element is actuatable by means of the filter insert (1), such that it is moved into its contact position when the filter insert (1) is inserted into the housing of the fuel filter.
 7. Fuel filter according to claim 6, characterized in that the switch element, in its intended installation position, is urged into its contact position by a force effect when the filter insert (1) is removed from the housing of the fuel filter.
 8. Fuel filter according to claim 6 or 7, characterized in that the switch element is urged into its contact position by gravity.
 9. Fuel filter according to claim 6 or 7, characterized in that the switch element is urged into its contact position by a spring.
 10. Fuel filter according to one of claims 6 to 9, characterized in that the switch element is insertable into the housing together with the filter insert (1).
 11. Fuel filter according to one of claims 6 to 10, characterized in that the switch element is constructed as part of the filter insert (1).
 12. Fuel filter according to one of the preceding claims, characterized in that the switch element has a defined electrical resistance that differs from that of the water that connects the two conductors (14) of the water level sensor (7).
 13. Fuel filter according to one of the preceding claims, characterized in that the switch element is constructed as a separate component.
 14. Switch element for creating a fuel filter according to one of the preceding claims, characterized in that the switch element is constructed according to one of the claims 3 to
 10. 15. Filter insert of a fuel filter according to one of the claims 1 to
 13. 16. Method for replacing a filter insert of a fuel filter, wherein the housing holding the filter insert is opened, a used filter insert is removed from the housing, an unused filter insert is inserted into the housing, and the housing is re-closed, characterized in that when the filter insert (1) is inserted, a switch element is moved in the fuel filter such that the switch element, due to its movement, alters the electrical resistance between two electrical conductors (14) of a water level sensor (7).
 17. Method according to claim 16, characterized in that two conductors (14) of a water level sensor (7) that are separated from each other are connected to one another when the switch element is being moved during insertion of the filter insert (1) and connects the two conductors (14) that were initially separated from each other.
 18. Method according to claim 16, characterized in that two conductors (14) of a water level sensor (7) that are connected to each other are separated by movement of a switch element during insertion of the filter insert (1) which separates the two conductors (14) that were initially connected to each other.
 19. Method according to one of the claims 16 to 18, characterized in that the switch element has a defined electrical resistance.
 20. Diagnostic method for checking a fuel filter, wherein the fuel filter has an replaceable filter insert, wherein the electrical resistance between two electrical conductors arranged in the fuel filter is altered, depending upon whether these two conductors are electrically connected to one another by water that is found in the fuel filter, and wherein the electrical resistance existing between the two conductors is automatically determined, wherein a first, so-called “short-circuit value” of the electrical resistance exists when the two conductors are electrically connected to one another by water that is in the fuel filter, and a second, so-called “insulation value” of the electrical resistance exists when the two conductors are electrically separated from one another, and wherein an electronic switch generates a switching signal at least then, when the “short-circuit value” is determined, characterized in that the electrical resistance between the two conductors (14) is automatically altered when the filter insert (1) is removed from the fuel filter, and that the electrical resistance between the two conductors (14) is automatically altered again when a filter insert (1) is inserted into the fuel filter.
 21. Diagnostic method according to claim 20, characterized in that the electrical resistance between the two conductors (14) automatically switches to the “short-circuit value” when the filter insert (1) is removed from the fuel filter.
 22. Diagnostic method according to claim 20, characterized in that the two conductors (14) are connected to one another by a defined electrical resistance when the filter insert (1) is inserted into the fuel filter, wherein the value of this electrical resistance, which is called the “filter insert value”, differs from both the “short-circuit value” and the “insulation value”.
 23. Diagnostic method according to one of the claims 20 to 22, characterized in that a warning signal is triggered when the “short-circuit value” is determined.
 24. Diagnostic method according to one of the claims 20 to 23, characterized in that a switch signal in the form of a blocking signal is transmitted to an electronic motor control unit when the “short-circuit value” is determined and that the motor control unit prevents the motor from starting when the blocking signal is present.
 25. Diagnostic method according to one of the claims 20 to 24, characterized in that the electronic switch is adjusted to a defined “filter insert value”, so that the warning signal or the blocking signal is triggered when an electrical resistance value that deviates from the “filter insert value” is measured between the two conductors (14). 